The present invention relates to a process for the stabilisation of the colour of green vegetables.
The green colour of vegetables is an extremely desirable culinary attribute in a number of products. This is particularly important in the development of chilled foods. However, the green colour is very sensitive to processing conditions involving heat and acid conditions and under these conditions the green colour can change to an undesirable olive brown colour.
The green colour of the vegetables is due to chlorophyll and this compound or its derivatives can be converted to compounds like pheophytins and pheophorbides which possess an olive brown colour. These conversions are mediated by thermal processing and acid pH conditions. The heating causes tissue damage which makes the chlorophyll molecules accessible to products and components present in the tissues or in the environment. Heat also produces organic acids which then react with the chlorophyll and replace the Mg in the molecule by H and this brings about the change in the colour. In most cases the external environment also has acid and this aggravates matters as far as retention of the green colour is concerned. The use of heat and acid are however very desirable in processing as far as destruction of microorganisms and enzymes is concerned. Low pH will also prevent the growth of the microorganisms.